A watchdog has backed claims that changes to data protection laws demanded in the wake of the phone-hacking scandal could have a "chilling effect" on investigative journalism.
Information Commissioner Christopher Graham said fears expressed over a recommendation of the Leveson Report were "legitimate" and should be considered carefully.
Lord Justice Leveson suggested media exemptions should be tightened so they could only hold data "necessary" for publication not only "with a view to" it being used.
Under the proposed reforms, journalists might also lose protection from "subject access" rights - forcing them to disclose data to individuals concerned and potentially exposing sources.
His verdict on media ethics also recommended enhanced powers for the Information Commissioner's Office (ICO) to prosecute the media, investigators and others for breaches.
The recommendations sparked immediate concerns, with Prime Minister David Cameron telling MPs he was "instinctively concerned" and other political leaders also expressing worries.
In its formal response to the report - which was published in November - the ICO said that while there was scope for reform, "we believe there is merit in having a broad exemption".
"The area of subject access is particularly problematic in that there are legitimate concerns about the 'chilling effect' Lord Justice Leveson's proposal might have on investigative journalism.
"This area will need very careful consideration. This again is a matter of balance of interests and is ultimately a matter for Parliament," it concluded.
The ICO also raised concerns that the recommended reforms to the Data Protection Act would move it "closer to becoming a mainstream statutory regulator of the press".
Such a role would "not only have implications for the press but would also have a significant impact on the ICO's strategy, operations and resources", it warned.
"If the ICO is to do more in relation to the press it is likely to be able to do less in areas of even greater public concern," it warned, calling for a wide-ranging consultation.
One Leveson recommendation welcomed by the ICO was the introduction of jail sentences for breaches of the Data Protection Act, for which it has long campaigned.
Custodial sanctions exist in legislation but have not been brought into force and the ICO said it hoped there would be "no further delay in implementing this recommendation", which was supported overwhelmingly in two Government consultations in 2006 and 2009.
Stronger penalties should not been seen as being "aimed wholly or mainly at the press", it said however, but at punishing wider misuse of personal data.